Long Term Evolution (LTE) is an improved universal mobile telecommunication system (UMTS) that provides higher data rate, lower latency and improved system capacity. In LTE systems, an evolved universal terrestrial radio access network includes a plurality of base stations, referred as evolved Node-Bs (eNBs), communicating with a plurality of mobile stations, referred as user equipment (UE). A UE may communicate with a base station or an eNB via the downlink and uplink. The downlink (DL) refers to the communication from the base station to the UE. The uplink (UL) refers to the communication from the UE to the base station. LTE is commonly marketed as 4G LTE, and the LTE standard is developed by 3GPP.
Enhancements to LTE systems are considered so that they can meet International Mobile Telecommunications Advanced (IMT-Advanced) fourth generation (4G) standard. One of the key enhancements is to support bandwidth up to 100 MHz and be backwards compatible with the existing wireless network system. Carrier aggregation (CA) is introduced to improve the system throughput. With carrier aggregation, the LTE-Advance system can support peak target data rates in excess of 1 Gbps in the downlink (DL) and 500 Mbps in the uplink (UL). Such technology is attractive because it allows operators to aggregate several smaller contiguous or non-continuous component carriers (CC) to provide a larger system bandwidth, and provides backward compatibility by allowing legacy users to access the system by using one of the CCs.
To support carrier aggregation, multiple radio frequency (RF) chains are required. Due to poor antenna or front-end isolation in the UE, a first radio signal transmitted by a first RF transceiver or its distorted version will be received by a second RF transceiver and vice versa. This mechanism of TX signal reciprocal mixing with a spur in the RX path is referred to as self-interference or TX self-jamming. If all system components were perfectly linear, the coupled version of the first radio signal would only act as an out-of-band jammer. However, nonlinear behavior of the RF receiver creates inter-modulation distortion (IMD) products that can land in the receiver band.
Digital cancellation of self-interference generated by RX nonlinearity requires estimation of several reference signals contributions. However, the number of reference signals significantly increases as nonlinearity order and front-end component frequency selectivity increase. As a result, the estimation of the reference signals contributions becomes more complex. Various methods of digital interference cancellation via a reference path have been proposed. The reference path, however, is fixed and cannot adapt to different RF configurations. An improve method of digital cancellation of self-interference generated by RX nonlinearity is sought to reduce computation complexity and to improve cancellation performance.